In response to the intensification of eco-friendly routes as a strategy to access compounds of interest, extraction based on hydrothermal technologies is an efficient method to obtain high yields of compounds present in lignocellulosic materials. Accordingly, this study investigated the effects of the combination of ultrasonic pretreatments (energy density, 1.23 × 10³–37.6 × 10³ J/cm³; reaction time, 15 and 60 min) and subcritical water hydrolysis (SWH) (temperature, 220°C; flow rate, 10–30 mL/min; and reaction time, 0.5–15 min) on sugar yield profile from residual biomass of rice, soybean, and pecan. A characterization of the sugars present in the hydrolyzed solutions by high-performance liquid chromatography (HPLC) and a physicochemical evaluation of biomasses by Fourier-transform infrared spectroscopy (FT-IR) was performed. The highest yield reported were 23.8/100 g biomass, 14.4/100 g biomass, and 6.0/100 g biomass for pecan shell, rice shell, and soybean straw, respectively. Cellobiose, glucose, xylose, and arabinose were quantified by the HPLC, as well as inhibitors and organic acids. FT-IR indicated the compositions of the fresh and pretreated samples. Appropriately, the combined application of ultrasonic and SWH methods supported the valorization and optimization of high potential materials generated in agricultural processing. GRAPHICAL ABSTRACT

Corn stover (CS) is a promising feedstock for producing fermentable sugars (FS) and ethanol due to its high holocellulose content. This study investigated the enhancement of FS production via enzymatic hydrolysis (EH) following steam explosion (SE) pretreatment of CS, aiming to improve ethanol yields through alcoholic fermentation. SE was conducted at 160 °C, 180 °C, and 200 °C for 2.5 and 10 min. EH was performed using 15 and 30 filter paper unit (FPU) enzyme loadings and 1% and 2% (w/w) substrate concentrations, applied to both untreated CS and pretreated CS (PCS). Fermentations with Saccharomyces cerevisiae were carried out at 30 °C and 120 rpm. The optimal SE condition (200 °C, 10 min) yielded 4.25 g of total sugars per 100 g CS. Under 30 FPU and 2% PCS, EH yielded 41.57 g/100 g PCS and 18.51 g/100 g CS. The combined SE + EH process reached 45.82 g/100 g PCS, about 2.5 times more than EH alone. The highest ethanol concentration and production rate were 15.54 g/L and 1.30 g/L·h, with a yield of 0.47 g/g. Under optimal conditions, fermentation achieved a conversion efficiency of 92.33%.